Derivative Instruments Derivative Instruments Affecting the Consolidated Statements of Income and Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in OCI on Derivative	$ 35.6	$ (23.8)	$ 3.6
Amount of Gain/(Loss) Reclassified from AOCI into Income	(2.4)	(0.2)	0.0
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Treasury Lock Agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in OCI on Derivative	35.6	(23.8)	3.6
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Treasury Lock Agreements [Member] \| Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income	(2.4)	(0.2)	0.0
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivative	(22.5)	14.1	6.3
Not Designated as Hedging Instrument [Member] \| Foreign Currency Forward Contracts [Member] \| Foreign Exchange Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivative	(22.5)	14.1	0.0
Not Designated as Hedging Instrument [Member] \| Foreign Currency Zero-Cost Collar Contracts [Member] \| Foreign Exchange Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in Income on Derivative	$ 0.0	$ 0.0	$ 6.3

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

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Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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